Targeting Option

[WhoIsTheGuest]

I tried holding X and then using tab to switch but nothing happen. The same for target cycling.

Because, it is called "Click" Filtering. Not Target Filtering. They are two different thing.
When X is pressed, and if you configured properly, your mouse-click will only select those filtered targets. It does not affect tab in anyway.
AFAIK, Click-Filtering only helps those with KB+M, while Target-Filtering settings only helps those with GamePad. I may be wrong about previous statement, but Click-Filtering is indeed working, because I am a healer and find it very helpful to target players in FATES.